World's Most Powerful Rocket Launches New US Spy Satellite

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A new spy satellite launched into orbit on a secret mission for
the U.S. military Friday (June 29), roaring spaceward atop the
world's most powerful rocket in use today.

The NROL-15 reconnaissance satellite blasted off from a launch
pad at Cape Canaveral Air Force Station in Florida at 9:15 a.m.
EDT (1315 GMT) to begin its classified mission for the National
Reconnaissance Office. It rode a towering
Delta 4-Heavy booster equipped with new RS-68A first stage
engines — the most powerful liquid hydrogen rocket engines ever
built, according to their manufactures.

Built by Pratt and Whitney Rocketdyne, the new RS-68A engines are
each capable of generating 702,000 pounds of thrust and are more
efficient than a previous design, the rocket engine builders
said, adding that the engine generates 36,000 more pounds of
thrust than its predecessor.Three of the new rocket engines made
their space launch debut in Friday's Delta 4-Heavy flight by
rocket provider United Launch Alliance.

The Delta 4-Heavy rocket is currently the largest and most
powerful rocket in service. The booster features three core
rocket boosters and is topped with a second stage to place
payloads into orbit. It is 235 feet tall (72 meters) and can
carry payloads of up to 24 tons into low-Earth orbit and 11 tons
to geosynchronous orbits.

Friday's launch came after several delays for the Delta 4-Heavy.
The rocket was initially slated to blast off on Thursday, but ULA
and Air Force officials pushed the launch back 24 hours due to
weather delays from Tropical Storm Debby.

During today's liftoff, a fuel valve problem prompted launch
controllers to repeatedly hold the countdown. But the glitch was
ultimately resolved, clearing the booster for flight.

The successful launch marked the second space mission in nine
days by ULA to orbit a classified payload for the U.S. military.
The company, a joint launch services endeavor by Boeing and
Lockheed Martin,
launched the NROL-38 spy satellite into orbit just last week
on June 20.

"Phew! 2 launches in 9 days. Who says things slow down in
summer!" ULA officials wrote in a Twitter post just after
liftoff.

ULA officials broadcast the secret NROL-15 satellite's launch
live, but cut the feed off four minutes after liftoff at the
request of NRO officials, a typical action for U.S.
reconnaissance satellite launches.

The next ULA launch will be an Atlas 5 rocket slated to loft
another NRO spy satellite into orbit in August. That mission is
expected to launch from the Vandenberg Air Force Station in
California.